1. Field of the Invention
This invention relates to a motion detection circuit for detecting motion in a video signal and a noise suppression circuit including the motion detection circuit.
2. Description of the Prior Art
A motion detection circuit for detecting motion in a video signal from a difference signal between the video signal and one-frame delayed video signal is known and a noise suppression circuit is also known. The noise suppression circuit includes the motion detection circuit, a circulation signal generation circuit for generating a circulation signal in accordance with the difference signal and the motion detection signal, and a subtractor for subtracting the circular signal from the video signal to output a noise suppressed video signal. Such a prior art motion detection circuit and a prior art noise suppression circuit are disclosed in Japanese patent application provisional publication No. 9-81754.
FIG. 9 is a block diagram of such a prior art noise suppression circuit including a prior art motion detection circuit.
The prior art motion detection circuit includes a frame memory 610 for generating a delayed video signal from the noise suppressed video signal Vo, a subtractor 602 for generating a difference signal (interframe difference signal) between the video signal Vi and the delayed video signal, a motion detection circuit 603 for detecting a motion from the video signal Vi and the delayed video signal to output a motion detection signal.
The noise suppression circuit further includes a subtractor 607 for generating the difference signal between the video signal Vi and the delayed video signal, a circulation amount determining circuit 608 for generating a circulation signal from the difference signal in accordance with the motion detection signal, and a subtractor 609 for obtaining a difference between the video signal Vi and the circulation signal to output a noise suppressed video signal Vo.
The aim of the present invention is to provide a superior motion detection circuit and a superior noise suppression circuit.
According to the present invention there is provided a first motion detection circuit including: a delay for generating a delayed video signal from a video signal, the delayed video signal being delayed by one frame from the video signal; a difference signal generation circuit for generating an interframe difference signal between the video signal and the delayed video signal; an edge detection signal generation circuit for detecting an edge from the video signal and the delayed video signal and generating an edge detection signal; and a motion judging circuit for judging a motion in the video signal at a target pixel from the interframe difference signal in accordance with the edge detection signal to output a motion detection signal.
The first motion detection circuit may further include a low-pass filter for low-pass-filtering the interframe difference signal and a selector for supplying either of an output of the low-pass filter or the interframe difference signal to the motion judging circuit as the interframe difference signal in accordance with a selection signal.
In a second motion detection circuit, the motion judging circuit mentioned in the first motion detection circuit may include a polarity deviation detecting circuit for detecting polarities of the interframe difference signal at each pixel of the video signal, detecting agreement of the polarities of all pixels at any of an upper left area of the target pixel, an upper right area of the target pixel, a lower left area of the target pixel, and a lower right area of the target pixel, and judging the motion in the interframe difference signal at the target pixel to be moving in the presence of the agreement, each of the upper left area, the upper right area, the lower left area, and the lower right area including Mxc3x97N pixels of the video signal, M and N being natural numbers. In this case, the upper left area, the upper right area, the lower left area, and the lower right area include the target pixel or outside and adjacent to the target pixel.
In a third motion detection circuit, the motion judging circuit mentioned in the second motion detection circuit may further include: a peripheral pixel comparing circuit for detecting polarities of the interframe difference signal at each pixel at a predetermined area around the target pixel, detecting the number of positive polarities of the interframe difference signal at the predetermined area and the number of negative polarities of the interframe difference signal at the predetermined area, obtaining a difference in the number between the positive and negative polarities and an absolute value of the difference, comparing the absolute value with first and second different references to output a comparing result indicative of either of moving, intermediate movement, or stopping, wherein the polarity deviation detection circuit changes the comparing result from the intermediate movement to stopping in accordance with the agreement to output the motion detection signal when the comparing result is indicative of the intermediate motion and outputs the motion detection signal with the comparing result unchanged when the comparing result is indicative of the moving and stopping.
In the third motion detection circuit, the motion judging circuit may further include another polarity deviation detecting circuit for detecting polarities of the differential signal at each pixel of the video signal, detecting agreement of the polarities of all pixels at any of the upper left area, the upper right area, the lower left area, and the lower right area every the target pixel, and judging the motion in the interframe difference signal at the target pixel to be moving in the presence of the agreement and a switch for either supplying an output of the polarity deviation detecting circuit or another polarity deviation detecting circuit in accordance with a switch control signal to output the motion detection signal.
In a fourth motion detection circuit, the motion judging circuit mentioned in the second motion detection circuit may further include: a peripheral pixel comparing circuit for detecting polarities of the interframe difference signal at each pixel at a predetermined area around the target pixel, detecting the number of positive polarities of the interframe difference signal at the predetermined area and the number of negative polarities of the interframe difference signal at each pixel at the predetermined area, obtaining a difference in the number between the positive and negative polarities and an absolute value of the difference, comparing the absolute value with Jxe2x88x921 references to output a J-valued first result, the polarity deviation detection circuit changes the first result to stopping in accordance with the agreement when the absolute value is judged to be an intermediate value among J values to output a second result, and the motion judging circuit further comprises a majority detection circuit including a memory for detecting a majority of the Q second results of the polarity deviation detection circuit at Q pixels around the target pixels and judging the motion in the interframe difference signal at the target pixel in accordance with the detected majority with deviation to a side of stopping to output the motion detection signal.
In a fifth motion detection circuit, the edge detection signal generation circuit mentioned in the first motion detection circuit may include a first edge detection circuit for detecting an edge from the video signal, a second edge detection circuit for detecting an edge from the delayed video signal, and a third edge detection circuit for detecting an edge from the video signal and the delayed video signal, a switch responsive to a selection signal for outputting either of an output of the first, second, or third edge detection circuit as the edge detection signal.
In the fifth motion detection circuit, the edge detection signal generation circuit may be further responsive to a width control signal indicative of values of m and n and the edge detection signal generation circuit detects the edge detection signal with a horizontal width of (2m+1) pixels and with a vertical width of (2n+1) pixels, n and m being positive integers.
In the second motion detection circuit, the values of the Mxc3x97N are controlled in accordance with the edge detection signal.
The fourth motion detection circuit may further include a switch responsive to the edge detection signal for either outputting the judging result of the majority detection circuit or the second result from polarity deviation detection circuit in accordance with the edge detection signal.
In the fourth motion detection circuit, the edge detection signal generation circuit includes a first edge detection circuit for detecting the edge from the video signal and the delayed video signal to generate a first edge signal (Edgm) with a first pixel width which is supplied to the polarity deviation detection circuit to control values of the Mxc3x97N in accordance with the first edge signal and a second edge detection circuit for detecting the edge from the video signal and the delayed video signal to generate a second edge signal (Edgs) with a second pixel width which is supplied to the majority detection circuit, a value of the first pixel width being different from a value of the second pixel width.
According to the present invention there is also provided a noise suppression apparatus including: a motion detection circuit including: a delay for generating a delayed video signal from a video signal, the delayed video signal being delayed by one frame from the video signal; an interframe difference signal generation circuit for generating an interframe difference signal between the video signal and the delayed video signal; a low-pass filter for low-pass-filtering the interframe difference signal; a switch for outputting either of an output of the low-pass filter or the interframe difference signal in accordance with a selection signal; an edge detection signal generation circuit for detecting an edge from the video signal and the delayed video signal and generating an edge detection signal; and a motion judging circuit for judging a motion in a target pixel of the video signal from an output of the switch in accordance with the edge detection signal; a circulation signal generation circuit including: a coefficient generation circuit for generating a coefficient k, kxe2x89xa60 less than 1 in accordance with a judging result of the motion judging circuit; and a multiplier for multiplying the video signal by the coefficient k to output a circulation signal; and a difference signal generation circuit for generating a difference signal between the circulation signal and the video signal to output a noise suppressed video signal, wherein the motion detection circuit may be replaced with each of the motion detection circuit mentioned above.